Aboard most warp-capable vessels, warp coils were fed by plasma conduits from the warp core reactor assembly. Venting the plasma from the nacelles made warp drive impossible until the nacelles could be replenished. (ENT: "Civilization") Nacelles were separated from the ship by large pylons, and usually housed a Bussard ramscoop at the fore end, primarily used for collecting hydrogen from space.

Even at sublight speeds serious impacts from weapons or other objects could spell disaster for a ship because of a feedback of energy throughout the vessel. The Enterprise-D was destroyed by such an impact in an alternate timeline when the USS Bozeman collided with one of Enterprise's warp nacelles. (TNG: "Cause and Effect")

According to Star Trek Blueprints, while the Constitution-class nacelles are powered up, they produce dangerous levels of radiation and crew members are not permitted to go up the Jefferies tubes that lead to the nacelles inside the nacelle pylons. [1]

According to the Spaceflight Chronology (p. 139), a three-nacelle configuration gives a third more power to the warp drive, greater acceleration and faster engagement. However, in the first experiments, the third nacelle accentuated discrepancies in the warp field causing warp vibrations. This created difficulties in steering, and would have resulted in the ship shaking itself apart at higher warp speeds. It was however noted that if the design was constructed perfectly it was possible for it to deliver what it promised.

The Star Trek: The Next Generation Technical Manual (pages 63, 65, and 66) states that the experiments with single and more than two nacelle designs, conducted in 2269, proved that having two nacelles was the optimal configuration for vessel control and power generation. On Galaxy-class starships, there was an emergency separation system for the nacelles. In the event the ship was damaged and unable to retain nacelle safely, explosive latches separated the nacelle from the pylon and lifted it up at thirty meters per second. If a nacelle was lost during warp flight, it will tear the ship apart, as the loss would cause different areas of the ship to travel at different warp factors.